There have been provided 3D image glasses including optical shutters which alternately transmit a right-eye image and a left-eye image constituting a 3D (three-dimensional) image, and the 3D image glasses enable a viewer to view stereoscopically a 3D image displayed by an image display device, i.e., a stereoscopic image constituted by a right-eye image and a left-eye image. Specifically, when the right-eye image is displayed, the 3D image glasses open a right optical shutter and close a left optical shutter, and when the left-eye image is displayed, the 3D image glasses close the right optical shutter and open the left optical shutter, thereby alternately transmitting the right-eye image and the left-eye image.
In order to make synchronization between operations of the image display device and the 3D image glasses, such as opening of the right optical shutter and closing of the left optical shutter when the right-eye image is displayed, there is frequently used a wireless signal transmission device. Examples of the image display device include television (TV) receivers and personal computers (PCs).
With reference to FIGS. 9 and 10, the following explains a conventional wireless signal transmission device and conventional 3D image glasses. FIG. 9 is a block diagram showing configurations of a conventional wireless signal transmission device and conventional 3D image glasses. FIG. 10 is a timing chart showing timing of control operation of the conventional wireless signal transmission device shown in FIG. 9.
As shown in FIG. 9, a wireless signal transmission device 101 receives, from an image display device 106, a sync signal indicative of timing for switching between display of a right-eye image and display of a left-eye image, signal indicative of which of the right-eye image and the left-eye image is to be displayed, optical shutter control data indicative of timing for controlling right and left optical shutters of 3D image glasses 110 etc. The wireless signal transmission device 101 generates a wireless transmission signal shown in (a) of FIG. 10 based on the sync signal and the optical shutter control data, and transmits the signal to the 3D image glasses 110 via wireless communications such as infrared (IR) communications and radio frequency (RF) communications. (b) of FIG. 10 shows timing at which the image display device 106 displays a right-eye image and a left-eye image.
When receiving the wireless transmission signal via a wireless signal reception section 111, the 3D image glasses 110 cause an optical shutter control timing generation section 112 to generate optical shutter control timing for controlling the optical shutters. Furthermore, an optical shutter control section 113 generates, in accordance with the generated optical shutter control timing, a right optical shutter control signal and a left optical shutter control signal shown in (c) and (d) of FIG. 10 so as to control the right optical shutter and the left optical shutter, respectively. The optical shutter control section 113 controls the right optical shutter and the left optical shutter in accordance with the generated right optical shutter control signal and the generated left optical shutter control signal, respectively.
That is, when the image display device 106 displays the right-eye image, the optical shutter control section 113 opens the right optical shutter and closes the left optical shutter, and when the image display device 106 displays the left-eye image, the optical shutter control section 113 closes the right optical shutter and opens the left optical shutter, thereby enabling a user to view the right-eye image only by the right eye and the left-eye image only by the left eye. Accordingly, alternately repeating opening and closing of the right optical shutter and the left optical shutter enables the user to view a 3D image stereoscopically.
In the above conventional technique, the wireless signal transmission device 101 transmits a wireless signal at timing for switching between the right-eye image and the left-eye image constituting a 3D image displayed by the image display device 106, i.e., timing for switching frames. For example, in a case where frame frequency is 100 Hz, the wireless signal transmission device 101 transmits a wireless signal per 10 ms, and the 3D image glasses 110 receive the wireless signal per 10 ms. Consequently, as the frame frequency is higher, power consumption of the wireless signal reception section 111 in the 3D image glasses 110 is likely to increase.
Furthermore, in most cases, the wireless signal transmission device 101 can always receive power supply from the image display device, whereas the 3D image glasses 110 use battery as a power source. That is, as the frame frequency is higher, operation time of the 3D image glasses 110 are shorter.
In order to deal with this problem, Patent Literature 1 proposes a wireless reception device used in 3D image glasses as mentioned below.
Patent Literature 1 discloses a technique relating to 3D image glasses including: a switch for switching between on and off of a power source supply circuit of a reception section; and switch control means. Specifically, the 3D image glasses are designed to detect the cycle of a wireless transmission signal from a transmission device, calculate, based on the cycle, a period in which the wireless transmission signal is not sent, and make the switch off during the period.
With the arrangement, the 3D image glasses make the switch off during a period in which the wireless transmission signal is not sent out of the aforementioned 10 ms for example, thereby reducing power consumption. Specifically, in a case where a period in which the wireless signal is received is 1 ms out of the aforementioned 10 ms, the remaining 9 ms is set to the period in which the wireless signal is not sent. Consequently, power consumption of the reception section can be reduced substantially one-tenth.